Speaking of tea , we often talk about full fermentation, semi-fermentation, and light fermentation. Is this the same fermentation as our common fermented foods such as yogurt, wine, vinegar, etc. What are the differences between them? Let's understand the tea Fermentation.
What is fermentation
Generally speaking, fermentation refers to a certain decomposition process of organisms to organic matter. Fermentation has long been recognized, but understanding its nature has been something that has been happening for nearly 200 years. Microbial physiology strictly defines fermentation: the process by which organisms are oxidatively degraded into oxidation products and release energy is collectively referred to as biological oxidation.
Fermentation defined in industrial production-industrial fermentation: Industrial production generally refers to all industrial production that depends on the life activities of microorganisms as fermentation, such as beer brewing and monosodium glutamate production. Fermentation in food: Fermented food refers to a type of food that is processed and manufactured by beneficial microorganisms, and has unique flavors, such as yogurt, cheese, wine, kimchi, soy sauce, vinegar, tempeh, rice wine, beer, wine, and so on.
Tea fermentation-biological oxidation
It is often said that Chinese tea is divided into six types of tea according to the degree of fermentation and the comprehensive production method. However, the term fermentation in the context of Chinese tea is completely different from the above-mentioned microbial fermentation. In tea, the same green leaf is processed into green tea , black tea , and oolong tea by controlling biological oxidation. This process is also incorrectly called fermentation. This process is more like a series of enzymatic reactions, and perhaps should be called biological oxidation. Biooxidation of tea is a series of oxidative processes of catechins promoted by oxidases present in the cell wall after cell wall damage.
In the cells of tea, catechins are present in the cell fluid, while oxidases are mainly present in the cell wall, not mainly in microorganisms, so the cell wall needs to be damaged. This naturally explains why fermented tea needs to be twisted. According to the different degree of oxidation of polyphenols, a full fermentation, a semi-fermentation and a light fermentation are distinguished. In black tea, the degree of oxidation of polyphenols is high, which is called full fermentation; the degree of oxidation of polyphenols in oolong tea is about half, which is called semi-fermentation.
For example, in the processing of black tea, the purpose of fermentation is to oxidize the catechins contained in the leaves. The color of the leaf changes from green to copper-red, producing a color unique to black tea. After the tea cell membrane is damaged, the polyphenols, amino acids, and other substances in the vacuole are gradually oxidized. At the same time, due to the oxidation of catechin, some substances in the leaves chemically react to produce the unique color and flavor quality of black tea.
The above is the basic meaning of fermentation often mentioned in Chinese tea. However, due to the large variety of teas in China, the variety of processing techniques and methods, and the definition of quality formation, there are different definitions of quality formation. In the process of making and quality formation of some teas, in addition to the above-mentioned fermentation in addition to the biological oxidation in addition to the enzymatic reaction In addition, some links will also involve microorganisms. For example, in addition to the enzymatic effect, the fermenting process of Pu'er tea ripe tea also involves microorganisms. After isolation and research, the main microorganisms are Aspergillus niger, Aspergillus oryzae, Aspergillus grayus, Rhizopus, Lactobacillus and yeast. Nevertheless, we still need to distinguish between fermentation involving microorganisms and fermentation in the sense of biological oxidation-otherwise, the conceptual ambiguity may easily lead to misunderstanding of the mechanism of tea quality formation.